Methods and systems for starting an engine

ABSTRACT

Methods and systems are provided for improving engine restart operations occurring during a transmission shift in a hybrid vehicle. Engine speed is controller during cranking and run-up to approach a transmission input shaft speed that is based on the future gear of the transmission shift. Engine speed is controlled via adjustments to spark, throttle, and/or fuel, to expedite engine speed reaching the synchronous speed.

CROSS REFERENCE TO RELATED APPLICATION

The present application is a divisional of U.S. patent application Ser.No. 14/462,405, entitled “METHODS AND SYSTEMS FOR STARTING AN ENGINE,”filed on Aug. 18, 2014. The entire contents of the above-referencedapplication are hereby incorporated by reference in its entirety for allpurposes.

FIELD

The present description relates to systems and methods for improvedengine speed control during an engine restart. The engine may beselectively coupled to an electrical machine and a transmission in ahybrid electric vehicle.

BACKGROUND AND SUMMARY

Hybrid electric vehicles (HEV's) utilize a combination of an internalcombustion engine with an electric motor to provide the power needed topropel a vehicle. This arrangement provides improved fuel economy over avehicle that has only an internal combustion engine in part due to theengine being shut down during times when the engine operatesinefficiently, or is not otherwise needed to propel the vehicle. Duringthese conditions, the vehicle is transitioned from an engine mode to anelectric mode where the electric motor is used to provide all of thepower needed to propel the vehicle. When the driver power demandincreases such that the electric motor can no longer provide enoughpower to meet the demand, or if the battery state of charge (SOC) dropsbelow a certain level, the engine is restarted. Vehicle propulsion isthen transitioned from an electric mode to an engine mode.

One method of enabling a smooth engine restart in an HEV powertrain isdisclosed by Tulpule et al. in US 20140088805. Therein, a disconnectclutch is disposed between an engine and a motor, which is operable todisconnect the engine from the motor. During an engine restart, thedisconnect clutch is disengaged so that the engine can be fueled toobtain a speed that matches the motor speed. Then, when the engine speedmatches the motor speed, the disconnect clutch is engaged to couple theengine and the motor to the drive shaft to meet the driver torquedemand. In another example disclosed by Sah et al. in U.S. Pat. No.8,628,451, engine speed and transmission input speed is synchronizedwhen an oncoming clutch is activated and an outgoing clutch isdeactivated.

However the inventors have recognized potential issues with such anapproach. As an example, if there is any speed difference between theengine and the impeller (or motor) speed, there may be substantialdriveline disturbance and NVH caused when the disconnect clutch isclosed. As such, there may be a difficulty in predicting the targetspeed at which the engine speed controller achieves synchronous speedfor the disconnect clutch to close. This difficulty arises from themotor being used to propel the vehicle while the engine is beingrestarted, which results in the motor speed changing constantly. Forexample, while the engine is at 150-200 rpm, the motor speed may be aslow as 600-700 rpm or as high as 2000 rpm. Predicting the target speedmay become more difficult if a transmission shift is requested duringthe engine restart. For example, if a driver requests increasedacceleration while the engine is being restarted, the transmission maycommand a downshift concurrent with the engine restart. If the enginespeed control is targeted to the higher speed of the gear existing whenthe engine restart was initiated, a higher level of airflow and fuel maybe commanded to accelerate the engine quickly to the higher speed. Ifthe transmission changes to the lower gear of the transmission shift atan inopportune time, the engine speed may overshoot the motor speed inthe reduced gear and lead to significant driveline disturbance. This canresult in vehicle surge and NVH issues. In the same way, if a driverrequests decreased acceleration while the engine is being restarted, thetransmission may command an upshift concurrent with the engine restart.If the engine speed control is targeted to the lower speed of the gearexisting when the engine restart was initiated, a lower level of airflowand fuel may be commanded to accelerate the engine quickly to the lowerspeed. If the transmission changes to the higher gear at an inopportunetime, there is a high likelihood that the engine speed will undershootthe motor speed in the higher gear and lead to significant drivelinedisturbance. As such, this can result in vehicle stall and NVH issues.

The inventors have recognized these issues and developed a method for ahybrid vehicle with an improved engine restart method. In one example, adriveline method comprises: during engine starting of a moving vehicle,the engine starting during a transmission shift transition, adjusting anengine speed based on a future gear of the transmission shift; andclosing a disconnect clutch before completion of the transmission shift.In this way, engine speed can be controlled to a synchronous speed basedon the future gear, reducing driveline disturbances.

As an example, while a vehicle is propelled via motor torque from anelectric motor, an engine restart request may be received. Accordingly,the engine may be cranked via the electric motor with a disconnectclutch coupled between the engine and motor at least partially open.Following cranking, engine fueling may be resumed and the engine speedmay be controlled to a synchronous speed after which the disconnectclutch may be closed. If the engine is restarted during a transmissionshift transition, the engine speed may be controlled to match atransmission input shaft speed based on the future gear of thetransmission following the transmission shift. For example, if theengine is restarted during a transmission downshift from a first, highergear to a second, lower gear, the downshift commanded due to theoperator requesting acceleration during the engine restart, the vehiclecontroller may adjust engine parameters to control the engine speedprofile towards the lower transmission input shaft speed expected in thesecond gear, rather than the higher transmission input shaft speedexpected in the first gear. Then, when the engine speed matches thesynchronous speed, the disconnect clutch may be closed, and thereafterthe transmission shift may be completed (e.g., the second gear may beengaged). This allows the engine speed to not undershoot the requiredsynchronous speed at the time of disconnect clutch closing, reducing NVHissues.

In this way, a quality of engine restarts in a hybrid electric vehicle,such as those performed concurrent to a transmission shift, may beimproved. By controlling the engine speed during a run-up phase of anengine restart so as to better match a future gear of the transmissionshift, rather than a current gear, NVH issues and driveline torquedisturbances associated with speed underestimation or overestimation canbe reduced. By predicting a synchronous speed expected at the time ofdisconnect clutch closing based on the nature of the transmission shift,vehicle stalls and bumps may be averted. Overall, a smoother enginerestart with reduced NVH issues is enabled, improving operator driveexperience.

It should be understood that the summary above is provided to introducein simplified form a selection of concepts that are further described inthe detailed description. It is not meant to identify key or essentialfeatures of the claimed subject matter, the scope of which is defineduniquely by the claims that follow the detailed description.Furthermore, the claimed subject matter is not limited toimplementations that solve any disadvantages noted above or in any partof this disclosure.

BRIEF DESCRIPTION OF THE DRAWINGS

The advantages described herein will be more fully understood by readingan example of an embodiment, referred to herein as the DetailedDescription, when taken alone or with reference to the drawings, where:

FIG. 1 is a schematic diagram of an engine;

FIG. 2 shows an example driveline configuration for a hybrid electricvehicle;

FIG. 3 shows an example method for restarting an engine of a hybridelectric vehicle during a transmission shift;

FIGS. 4-5 show example engine restart sequences occurring during andoutside of a transmission shift transition.

DETAILED DESCRIPTION

Methods and systems are provided for enabling smooth engine restarts ina hybrid electric vehicle, such as the vehicle system of FIGS. 1-2.During conditions when an engine restart operation overlaps with atransmission shift event, engine speed may be controlled so as to run-upthe engine to a speed that better matches the future gear of thetransmission shift event. A vehicle controller may be configured toperform a control routine, such as the example routine of FIG. 3, tocrank the engine using motor torque while slipping a disconnect clutchcoupled between the engine and the motor. After resuming engine fueling,the vehicle controller may control the engine speed profile so as toraise the engine speed to a predicted synchronous speed that is based onthe gear of the transmission after the transmission shift is completed.The engine speed may be controlled via adjustments to engine parameterssuch as throttle angle and spark timing. Example engine restartsequences are shown at FIGS. 4-5. In this way, a smooth engine restartis achieved.

Referring to FIG. 1, internal combustion engine 10, comprising aplurality of cylinders, one cylinder of which is shown in FIG. 1, iscontrolled by electronic engine controller 12. Engine 10 includescombustion chamber 30 and cylinder walls 32 with piston 36 positionedtherein and connected to crankshaft 40. Flywheel 97 and ring gear 99 arecoupled to crankshaft 40. Starter 96 includes pinion shaft 98 and piniongear 95. Pinion shaft 98 may selectively advance pinion gear 95 toengage ring gear 99. Starter 96 may be directly mounted to the front ofthe engine or the rear of the engine. In some examples, starter 96 mayselectively supply torque to crankshaft 40 via a belt or chain. In oneexample, starter 96 is in a base state when not engaged to the enginecrankshaft.

Combustion chamber 30 is shown communicating with intake manifold 44 andexhaust manifold 48 via respective intake valve 52 and exhaust valve 54.Each intake and exhaust valve may be operated by an intake cam 51 and anexhaust cam 53. The position of intake cam 51 may be determined byintake cam sensor 55. The position of exhaust cam 53 may be determinedby exhaust cam sensor 57.

Fuel injector 66 is shown positioned to inject fuel directly intocylinder 30, which is known to those skilled in the art as directinjection. Alternatively, fuel may be injected to an intake port, whichis known to those skilled in the art as port injection. Fuel injector 66delivers liquid fuel in proportion to the pulse width of signal FPW fromcontroller 12. Fuel is delivered to fuel injector 66 by a fuel system(not shown) including a fuel tank, fuel pump, and fuel rail (not shown).Fuel injector 66 is supplied operating current from driver 68 whichresponds to controller 12. In addition, intake manifold 44 is showncommunicating with optional electronic throttle 62 which adjusts aposition of throttle plate 64 to control air flow from air intake 42 tointake manifold 44. In one example, a high pressure, dual stage, fuelsystem may be used to generate higher fuel pressures. In some examples,throttle 62 and throttle plate 64 may be positioned between intake valve52 and intake manifold 44 such that throttle 62 is a port throttle.

Distributorless ignition system 88 provides an ignition spark tocombustion chamber 30 via spark plug 92 in response to controller 12.Universal Exhaust Gas Oxygen (UEGO) sensor 126 is shown coupled toexhaust manifold 48 upstream of catalytic converter 70. Alternatively, atwo-state exhaust gas oxygen sensor may be substituted for UEGO sensor126.

Vehicle wheel brakes or regenerative braking via a driveline integratedstarter/generator (DISG) may be provided when brake pedal 150 is appliedvia foot 152. Brake pedal sensor 154 supplies a signal indicative ofbrake pedal position to controller 12. Foot 152 is assisted by brakebooster 140 applying vehicle brakes.

Converter 70 can include multiple catalyst bricks, in one example. Inanother example, multiple emission control devices, each with multiplebricks, can be used. Converter 70 can be a three-way type catalyst inone example.

Controller 12 is shown in FIG. 1 as a conventional microcomputerincluding: microprocessor unit 102, input/output ports 104, read-onlymemory 106, random access memory 108, keep alive memory 110, and aconventional data bus. Controller 12 is shown receiving various signalsfrom sensors coupled to engine 10, in addition to those signalspreviously discussed, including: engine coolant temperature (ECT) fromtemperature sensor 112 coupled to cooling sleeve 114; a position sensor134 coupled to an accelerator pedal 130 for sensing force applied byfoot 132; a measurement of engine manifold pressure (MAP) from pressuresensor 122 coupled to intake manifold 44; an engine position sensor froma Hall effect sensor 118 sensing crankshaft 40 position; a measurementof air mass entering the engine from sensor 120; and a measurement ofthrottle position from sensor 58. Barometric pressure may also be sensed(sensor not shown) for processing by controller 12. Engine positionsensor 118 produces a predetermined number of equally spaced pulsesevery revolution of the crankshaft from which engine speed (RPM) can bedetermined.

In some examples, the engine may be coupled to an electric motor/batterysystem in a hybrid vehicle as shown in FIG. 2. Further, in someexamples, other engine configurations may be employed, for example adiesel engine.

During operation, each cylinder within engine 10 typically undergoes afour stroke cycle: the cycle includes the intake stroke, compressionstroke, expansion stroke, and exhaust stroke. During the intake stroke,generally, the exhaust valve 54 closes and intake valve 52 opens. Air isintroduced into combustion chamber 30 via intake manifold 44, and piston36 moves to the bottom of the cylinder so as to increase the volumewithin combustion chamber 30. The position at which piston 36 is nearthe bottom of the cylinder and at the end of its stroke (e.g. whencombustion chamber 30 is at its largest volume) is typically referred toby those of skill in the art as bottom dead center (BDC). During thecompression stroke, intake valve 52 and exhaust valve 54 are closed.Piston 36 moves toward the cylinder head so as to compress the airwithin combustion chamber 30. The point at which piston 36 is at the endof its stroke and closest to the cylinder head (e.g. when combustionchamber 30 is at its smallest volume) is typically referred to by thoseof skill in the art as top dead center (TDC). In a process hereinafterreferred to as injection, fuel is introduced into the combustionchamber. In a process hereinafter referred to as ignition, the injectedfuel is ignited by known ignition means such as spark plug 92, resultingin combustion. During the expansion stroke, the expanding gases pushpiston 36 back to BDC. Crankshaft 40 converts piston movement into arotational torque of the rotary shaft. Finally, during the exhauststroke, the exhaust valve 54 opens to release the combusted air-fuelmixture to exhaust manifold 48 and the piston returns to TDC. Note thatthe above is shown merely as an example, and that intake and exhaustvalve opening and/or closing timings may vary, such as to providepositive or negative valve overlap, late intake valve closing, orvarious other examples.

FIG. 2 is a block diagram of a vehicle 201 and vehicle driveline 200.Driveline 200 may be powered by engine 10. Engine 10 may be started withan engine starting system shown in FIG. 1 or via a driveline integratedstarter/generator DISG 240. Further, engine 10 may generate or adjusttorque via torque actuator 204, such as a fuel injector, throttle, etc.

An engine output torque may be transmitted to an input side of dual massflywheel (DMF) 232. Engine speed as well as dual mass flywheel inputside position and speed may be determined via engine position sensor118. Dual mass flywheel 232 may include springs 253 and separate masses254 for dampening driveline torque disturbances. The output side of dualmass flywheel 232 is shown being mechanically coupled to the input sideof disconnect clutch 236. Disconnect clutch 236 may be electrically orhydraulically actuated. A position sensor 234 is positioned on thedisconnect clutch side of dual mass flywheel 232 to sense the outputposition and speed of the dual mass flywheel 232. The downstream side ofdisconnect clutch 236 is shown mechanically coupled to DISG input shaft237.

When disconnect clutch 236 is fully engaged (or closed), the engineoutput shaft is coupled to the DISG, allowing the motor to start theengine, such as during an engine restart. In contrast, when disconnectclutch 236 is fully disengaged (or open), the engine may be disconnectedfrom the electric machine. Disconnecting the engine from the electricmachine allows the electric machine to propel the vehicle without havingto overcome parasitic engine losses. Further still, the disconnectclutch may be partially engaged and slipped to vary the disconnectclutch's torque capacity. As elaborated at FIG. 3, controller 12 may beconfigured to adjust the amount of torque transmitted to crank theengine by adjusting the disconnect clutch 236 during an engine restart.The clutch may then be closed when the engine speed reaches asynchronous speed that is based on a current or predicted transmissioninput shaft speed.

DISG 240 may be operated to provide torque to driveline 200 or toconvert driveline torque into electrical energy to be stored in electricenergy storage device 275. DISG 240 has a higher output torque capacitythan starter 96 shown in FIG. 1. Further, DISG 240 directly drivesdriveline 200 or is directly driven by driveline 200. There are nobelts, gears, or chains to couple DISG 240 to driveline 200. Rather,DISG 240 rotates at the same rate as driveline 200. Electrical energystorage device 275 may be a battery, capacitor, or inductor. Thedownstream side of DISG 240 is mechanically coupled to the impeller 285of torque converter 206 via shaft 241. The upstream side of the DISG 240is mechanically coupled to the disconnect clutch 236. Torque converter206 includes a turbine 286 to output torque to transmission input shaft270. Transmission input shaft 270 mechanically couples torque converter206 to automatic transmission 208. Torque converter 206 also includes atorque converter bypass lock-up clutch 212 (TCC). Torque is directlytransferred from impeller 285 to turbine 286 when TCC is locked. TCC iselectrically operated by controller 12. Alternatively, TCC may behydraulically locked. In one example, the torque converter may bereferred to as a component of the transmission. Torque converter turbinespeed and position may be determined via position sensor 239. In someexamples, 238 and/or 239 may be torque sensors or may be combinationposition and torque sensors.

When torque converter lock-up clutch 212 is fully disengaged, torqueconverter 206 transmits engine torque to automatic transmission 208 viafluid transfer between the torque converter turbine 286 and torqueconverter impeller 285, thereby enabling torque multiplication. Incontrast, when torque converter lock-up clutch 212 is fully engaged, theengine output torque is directly transferred via the torque converterclutch to an input shaft (not shown) of transmission 208. Alternatively,the torque converter lock-up clutch 212 may be partially engaged,thereby enabling the amount of torque directly relayed to thetransmission to be adjusted. The controller 12 may be configured toadjust the amount of torque transmitted by torque converter 206 byadjusting the torque converter lock-up clutch 212 in response to variousengine operating conditions, or based on a driver-based engine operationrequest.

Automatic transmission 208 includes gear clutches (e.g., gears 1-6) 211and forward clutch 210. The gear clutches 211 and the forward clutch 210may be selectively engaged to propel a vehicle. Torque output from theautomatic transmission 208 may in turn be relayed to rear wheels 216 topropel the vehicle via output shaft 260. Specifically, automatictransmission 208 may transfer an input driving torque at the input shaft270 responsive to a vehicle traveling condition before transmitting anoutput driving torque to the rear wheels 216. Torque may also bedirected to front wheels 217 via transfer case 261.

Further, a frictional force may be applied to wheels 216 by engagingwheel brakes 218. In one example, wheel brakes 218 may be engaged inresponse to the driver pressing his foot on a brake pedal (not shown).In other examples, controller 12 or a controller linked to controller 12may apply wheel brakes. In the same way, a frictional force may bereduced to wheels 216 by disengaging wheel brakes 218 in response to thedriver releasing his foot from a brake pedal. Further, vehicle brakesmay apply a frictional force to wheels 216 via controller 12 as part ofan automated engine stopping procedure.

A mechanical oil pump 214 may be in fluid communication with automatictransmission 208 to provide hydraulic pressure to engage variousclutches, such as forward clutch 210, gear clutches 211, and/or torqueconverter lock-up clutch 212. Mechanical oil pump 214 may be operated inaccordance with torque converter 206, and may be driven by the rotationof the engine or DISG via input shaft 241, for example. Thus, thehydraulic pressure generated in mechanical oil pump 214 may increase asan engine speed and/or DISG speed increases, and may decrease as anengine speed and/or DISG speed decreases.

Controller 12 may be configured to receive inputs from engine 10, asshown in more detail in FIG. 1, and accordingly control a torque outputof the engine and/or operation of the torque converter, transmission,DISG, clutches, and/or brakes. As one example, an engine torque outputmay be controlled by adjusting a combination of spark timing, fuel pulsewidth, fuel pulse timing, and/or air charge, by controlling throttleopening and/or valve timing, valve lift and boost for turbo- orsuper-charged engines. In the case of a diesel engine, controller 12 maycontrol the engine torque output by controlling a combination of fuelpulse width, fuel pulse timing, and air charge. In all cases, enginecontrol may be performed on a cylinder-by-cylinder basis to control theengine torque output. Controller 12 may also control torque output andelectrical energy production from DISG by adjusting current flowing toand from field and/or armature windings of DISG as is known in the art.Controller 12 also receives driving surface grade input information frominclinometer 281.

When idle-stop conditions are met, when the vehicle speed is close tozero, or other engine shutdown conditions are met, such as when theengine is shutdown at higher speeds (e.g. during electric only or brakeregeneration operation), controller 12 may initiate engine shutdown byshutting off fuel and spark to the engine. However, the engine maycontinue to rotate in some examples. Further, to maintain an amount oftorsion in the transmission, the controller 12 may ground rotatingelements of transmission 208 to a case 259 of the transmission andthereby to the frame of the vehicle.

If the vehicle is being launched from zero speed, a wheel brake pressuremay also be adjusted during the engine shutdown, based on thetransmission clutch pressure, to assist in tying up the transmissionwhile reducing a torque transferred through the wheels. Specifically, byapplying the wheel brakes 218 while locking one or more engagedtransmission clutches, opposing forces may be applied on transmission,and consequently on the driveline, thereby maintaining the transmissiongears in active engagement, and torsional potential energy in thetransmission gear-train, without moving the wheels. In one example, thewheel brake pressure may be adjusted to coordinate the application ofthe wheel brakes with the locking of the engaged transmission clutchduring the engine shutdown. As such, by adjusting the wheel brakepressure and the clutch pressure, the amount of torsion retained in thetransmission when the engine is shutdown may be adjusted. When restartconditions are satisfied, and/or a vehicle operator wants to launch thevehicle, controller 12 may reactivate the engine by resuming cylindercombustion.

Thus, in the vehicle system of FIGS. 1-2, the vehicle is equipped with amodular hybrid transmission (MHT). As described above, the powertrainhas a conventional step ratio automatic transmission in which a “frontmodule”, with the electric machine (the DISG) and the disconnect clutch,is inserted between the engine and the transmission input. The DISG isthereby permanently connected to the transmission input (e.g., to thetorque converter impeller or to a launch clutch). The disconnect clutchis then used to connect or disconnect the engine, thereby makingelectric only drive possible.

As such, engine starts are accomplished by controlling the disconnectclutch to vary torque provided from the electric machine to crank theengine. When the engine is rotated a sufficient number of crank angledegrees, fuel and spark is then applied to accelerate the enginecrankshaft, and/or flywheel, to the synchronous, or output, speed of thedisconnect clutch. As the output side of the disconnect clutch isrigidly connected to the transmission input through the electric machinerotor, the disconnect clutch output is equal to the transmission inputspeed. To reduce drive line disturbance during the engine restart event,as described below, a controller may reduce disconnect clutch torquecapacity or maintain it at a level when significant clutch slip allowsthe engine to run up to the synchronous speed. At that point thedisconnect clutch can be fully applied or engaged without noticeabletorque disturbance.

As such, if there is any speed difference between the engine and theimpeller speed, driveline disturbances are caused when the disconnectclutch is closed. However, while the engine is being restarted, themotor continues to propel the vehicle. This results in a constant changein the motor speed. Consequently, it may be difficult to accuratelypredict the target synchronous speed at which the disconnect clutch willclose. If the vehicle operator requests acceleration or decelerationwhile the engine is being restarted, it may be result in a transmissionshift which may make predicting the target speed even more difficult.For example, if the engine is restarted in the middle of a transmissiondownshift transition, the vehicle controller may close the disconnectclutch at a synchronous speed based on the current gear. However, if thetransmission downshift occurs before the disconnect clutch is closed,the engine may have already increased airflow and fueling to quicklyaccelerate to the higher speed of the higher gear. Consequently, at thetime of disconnect clutch closing, the engine speed may overshoot,resulting in a driveline disturbances experienced by the vehicleoperator as a bump of clunk. Likewise, if the engine restart occurs inthe middle of a transmission upshift transition, there is a possibilityof the engine speed undershooting the target speed at the time of clutchengagement, resulting in a driveline disturbance that causes a vehiclestall.

As elaborated herein, with reference to the methods of FIG. 3, acontroller may smoothly restart an engine during an engine restart usingthe system of FIGS. 1-2. Therein, during engine starting of a movingvehicle, such as a hybrid vehicle being propelled via motor torque froman electric motor, and wherein the engine is started during atransmission shift transition, an engine speed is adjusted based on afuture gear of the transmission shift, and the disconnect clutch isclosed before completion of the transmission shift. In particular, theengine speed is adjusted based on the future gear of the transmissionshift so that the engine speed is raised to a synchronous speed of thefuture gear of the transmission shift. The controller may adjust theengine speed by adjusting parameters such as spark timing, throttleangle, and fuel injection based on the future gear of the transmissionshift. In this way, a smooth engine restart is enabled with reduceddriveline disturbances.

Now turning to FIG. 3, an example method 300 is provided for smoothlystarting an engine. In the present example, the engine is restartedwhile the vehicle is moving using motor torque in an electric drive modeto transition the vehicle to being operated in a hybrid mode based onthe user's torque demands.

At 302, the routine includes confirming that an engine restart requesthas been received. The engine restart may be requested responsive to anincreased torque demand from a vehicle operator. As another example, anengine restart may be requested responsive to a system battery state ofcharge being lower than a threshold. If an engine restart request isconfirmed, routine 300 proceeds to 306. Otherwise, the routine proceedsto 304 where the engine is maintained shut down while the vehicle iscontinued to be propelled via motor torque.

At 306, the routine includes cranking the engine via a motor. Inparticular, the engine is cranked from rest (that is, 0 rpm). Then, oncethe engine has been cranked to a threshold speed, engine fueling may beresumed so that cylinder combustion can be used to spin the engine andrun up the engine speed. In one example, the engine may be cranked usingmotor torque from the DISG. In an alternate example, the engine may becranked using at least some motor torque from a starter motor. Crankingthe engine via the motor may include transiently increasing the torqueoutput of the motor so as to provide sufficient torque to propel thevehicle and crank the engine. At 308, while cranking the engine via themotor, a disconnect clutch coupled between the engine and the motor inthe driveline may be at least partially disengaged. That is, the enginemay be cranked via the motor with the disconnect clutch at leastpartially open. The disconnect clutch being at least partiallydisengaged or open includes the disconnect clutch being slipped. Adegree of slippage of the disconnect clutch may be adjusted based onengine speed. For example, the degree of slippage may be adjusted basedon the rate of change of engine speed during the cranking, that is,based on the engine acceleration. In another example, the degree ofslippage may be adjusted based on a difference between the engine speedand the motor speed across the disconnect clutch. By partiallydisengaging the disconnect clutch, and varying the degree of slippage ofthe clutch, the clutch's torque capacity is varied while the engine isstarted, without a loss of output torque delivered to the drive wheels.

In one example, the engine may be cranked to first speed, such as to150-200 rpm, unfueled, using motor torque with the disconnect clutchcoupled between the engine and the motor at least partially disengaged.When the engine cranking speed reaches a threshold speed, such as at orabove 150-200 rpm, engine fueling is resumed.

At 310, it may be determined if there is a transmission shift that ispending. The transmission may be a fixed gear ratio transmission havinga plurality of gears. The transmission may be shifted from a first gearto a second gear in response to vehicle conditions. In one example, atransmission shift may be commanded after the engine restart has beeninitiated due to a change in operator torque demand during the restart.For example, in response to an operator demand for more acceleration, atransmission upshift may be commanded. In another example, in responseto an operator demand for deceleration (or less acceleration), atransmission downshift may be commanded. In response to the transmissionshift command, the transmission may be transitioned from a first,current gear to a second, future gear while the engine is beingrestarted. In other words, the transmission shift transition and theengine speed run-up during the restart may at least partially overlap.

If a transmission shift is not pending, then at 312, the routineincludes determining a target engine synchronous speed based on thecurrent transmission gear. For example, an engine speed matching atransmission shaft input speed at the current gear may be determined tobe the target speed. Then, at 316, the engine speed may be adjustedduring the run-up phase of the engine start to being the engine speed upto the determined target speed. This may include adjusting one or moreof spark timing (at 320), throttle angle (at 318) and fuel injectionbased on the current gear of the transmission.

In one example, the spark and throttle adjustment performed to controlthe engine speed to the target synchronous motor speed may be based onthe impeller speed. In particular, at lower impeller speeds, sparktiming retard may be increased (e.g., spark may be heavily retarded) andthrottle opening may be decreased (e.g., throttle may be closed on everyevent) to avoid raising the engine speed above the target speed forimproved driveability. In comparison, at higher impeller speeds, sparktiming retard may be decreased (e.g., spark may be advanced) andthrottle opening may be increased (e.g., throttle may be opened on everyevent) to raise the engine speed to the target speed quickly.

If a transmission shift is pending, then at 314, the routine includesdetermining a target engine synchronous speed based on the future gearof the transmission shift. That is, where the transmission is beingshifted from a first gear to a second gear, the target speed may bedetermined based on the second gear and not the first gear, even if theengine restart was initiated while the transmission was in the firstgear. Then, at 316, the engine speed may be adjusted to a synchronousspeed of the future gear (herein the second gear) of the transmissionshift. This includes adjusting one or more of spark timing (at 320),throttle angle (at 318) and fuel injection based on the future gear ofthe transmission shift.

As one example, the transmission shift may be a transmission downshift(e.g., commanded responsive to a demand for increased acceleration),wherein the future gear is a lower gear having a lower synchronous speedsetting relative to the current gear which is a higher gear with ahigher synchronous speed setting. Herein, the adjusting may include oneof decreasing an amount of spark retard, increasing an amount of sparkadvance, decreasing the throttle angle, and decreasing fuel injectionbased on the synchronous speed of the future gear of the transmissiondownshift being lower. In another example, the transmission shift may bea transmission upshift (e.g., commanded responsive to a demand fordecreased acceleration), wherein the future gear is a higher gear havinga higher synchronous speed setting relative to the current gear which isa lower gear with a lower synchronous speed setting. Herein, theadjusting may include one of increasing an amount of spark retard (ordecreasing an amount of spark advance), increasing the throttle angle,and increasing fuel injection based on the synchronous speed of thefuture gear of the transmission upshift being higher.

In one example, the adjusting of engine fuel, spark and/or airflow toprovide the desired engine speed profile to the target synchronous speedmay be further based on a derivative of the current engine speed afterresuming engine fueling (indicative of the engine speed trajectory) anda derivative of the current motor speed after resuming engine fueling(indicative of the motor speed trajectory). This allows the enginetorque to be more accurately adjusted responsive to the predictedsynchronous motor speed. In particular, based on the engine speedtrajectory and the motor speed trajectory, it may be determined if theengine speed will match the synchronous motor speed at desired time ofclutch engagement. As such, if the disconnect clutch is engaged whilethe engine speed and motor speed are not matched, driveline torquedisturbances may occur which can lead to significant NVH issues (e.g.,sudden jerks). In one example, if the engine speed is expected to belower than the predicted motor speed at a desired time of clutchengagement, or if the predicted synchronous motor speed is higher thanthe current motor speed, the controller may adjust one or more fuel,air, and spark to the engine to increase engine acceleration. Forexample, fuel and/or air may be transiently increased and spark timingmay be retarded to increase engine acceleration. Herein, by increasingfueling and/or retarding spark timing, a difference between the enginespeed and the motor speed is reduced. As another example, if the enginespeed is expected to be higher than the predicted motor speed at adesired time of clutch engagement, or if the predicted synchronous motorspeed is lower than the current motor speed, the controller may adjustone or more fuel, air, and spark to the engine to decrease engineacceleration. For example, fuel and/or air may be transiently decreasedand spark timing may be advanced to decrease engine acceleration.

In one example, the spark and throttle adjustment performed to controlthe engine speed to the target synchronous motor speed of the futuregear may be based on the impeller speed. In particular, at lowerimpeller speeds, spark timing retard may be increased (e.g., spark maybe heavily retarded) and throttle opening may be decreased (e.g.,throttle may be closed on every event) to avoid raising the engine speedabove the target speed for improved driveability. In comparison, athigher impeller speeds, spark timing retard may be decreased (e.g.,spark may be advanced) and throttle opening may be increased (e.g.,throttle may be opened on every event) to raise the engine speed to thetarget speed quickly.

As such, when the engine speed is below the synchronous speed, theengine may be spinning with the disconnect clutch at least partiallyopen. That is, while the engine speed is adjusted to the synchronousspeed, the disconnect clutch may be maintained partially disengaged witha degree of slippage of the partially disengaged or partially opendisconnect clutch continually adjusted based on the engine speedrelative to the synchronous speed. For example, when the differencebetween the engine speed and the synchronous speed is higher, the degreeof slippage may be increased, and as the engine speed approaches thesynchronous speed, the degree of slippage may be decreased.

In some examples, the engine speed profile or trajectory to the targetspeed may also be controlled. For example, engine speed may be initiallybe raised from the first speed (when engine fueling is resumed) to asecond speed (which is below the target speed, but within a threshold ofthe second speed), at a faster rate by increasing engine fueling at ahigher rate, opening the throttle angle more, and/or retarding sparktiming by a larger amount. This allows the engine to be quicklyaccelerated to a second speed that is within a threshold of the targetspeed. Then, once the engine speed is at the second speed and within athreshold of the target speed, engine speed may be raised at a slowerrate from the second speed to the target synchronous speed, such as byincreasing engine fueling at a lower rate, decreasing the throttleangle, and/or advancing spark timing. This allows the engine to begradually, and more deliberately, moved to the target speed. As such,this may improve the accuracy of matching the engine speed to thesynchronous speed, thereby improving engine restart quality.

In some examples, the controller may also use engine speed feedback tocontrol the engine restart speed profile. In particular, since the slipspeed is closely related to the engine speed profile, by controlling theslip speed profile, a desired engine speed profile to the targetsynchronous speed may be achieved. The clutch slip may be related to theengine speed profile in that slip is equal to the disconnect clutchinput speed (neglecting any DMF oscillation) minus the disconnect clutchoutput speed. Thus, the DISG speed may be used as the input speed andslip may be adjusted to achieve a desired engine speed profile (e.g.,desired rate of increase in engine speed) to the target speed.

It will be appreciated that the target speed may also change duringengine speed run-up. For example, engine control may be initiated whenthere is no transmission shift pending. Accordingly, engine speedcontrol may be adjusted to a first target speed based on a firstpredicted transmission input shaft speed corresponding to a situationwhere there is no transmission shift. Therein, spark and throttle may beadjusted to a first setting (e.g., a first rate, a first amount of sparkretard and a first amount of throttle opening). Due to a transmissionshift occurring while the engine speed is being run-up to the firsttarget speed, the target speed may be changed responsive to the shift toa second target speed corresponding to a predicted transmission inputshaft speed following the shift. Thus, in the middle of the engine speedcontrol, the target speed may be changed from the first target speed tothe second target speed via readjusting of spark and throttle settings.For example, spark and throttle may be readjusted from the first settingto a second setting (e.g., a second rate, a second amount of sparkretard and a second amount of throttle opening). Thus, during therun-up, the engine speed trajectory may change as the target speedchanges from the first target speed to the second target speed.

At 322, it may be determined if the synchronous speed has been reached.If not, at 324, engine fueling, throttle angle and/or spark timing isadjusted to bring the engine speed to the synchronous speed while thedisconnect clutch is maintained at least partially disengaged with theclutch being slipped. In addition, the slippage may continue to beadjusted based on the engine speed relative to the motor speed (ortarget synchronous speed).

If the engine speed is at or within a threshold distance of the targetsynchronous speed, then at 326, the routine includes closing thedisconnect clutch. After closing the disconnect clutch, the hybridvehicle may be propelled with at least engine torque. For example, thehybrid vehicle may be transitioned from an electric mode to a hybridmode.

In one example, a hybrid vehicle controller may control an enginerestart speed, during an engine restart, to a predicted transmissioninput shaft speed. In particular, where the transmission shift includesshifting a fixed gar ratio transmission from a first gear (the currentgear) to a second gear (the future gear) in response to vehicleconditions, the predicted transmission input shaft speed may be based ontransmission input shaft speed after beginning to engage the second gearbut before the second gear is fully engaged. The shifting of thetransmission may have been commanded after the engine start wasinitiated. Herein, the transmission shift may be a transmissiondownshift, with the second gear being lower than the first gear and withthe predicted transmission input shaft speed (at the second gear) beinglower than the transmission input shaft speed at the first gear. Whilepropelling the vehicle with motor torque, the controller may crank theengine to a first speed, unfueled, using motor torque with thedisconnect clutch between the motor and the engine at least partiallydisengaged. Then, the controller may adjust one or more of enginefueling (e.g., increasing engine fueling), throttle angle (e.g.,increase throttle angle to increase throttle opening), and spark timing(e.g., retard spark timing) to raise the engine restart speed from thefirst speed to the predicted transmission input shaft speed with thedisconnect clutch maintained at least partially disengaged. Thedisconnect clutch may be continuously slipped while the engine speedremains below the predicted transmission input shaft speed, a degree ofslippage of the disconnect clutch modulated based on the engine restartspeed relative to the predicted transmission input shaft speed. Forexample, the degree of slippage may be increased as the differenceincreases. Then, once the engine speed matches the predictedtransmission input shaft speed, the disconnect clutch may be closed, andthen the second gear may be engaged. Thus, the disconnect clutch may beclosed after beginning to engage the second gear but before the secondgear is fully engaged.

In this way, engine restarts may be enabled with reduced drivelinetorque disturbances, even if a transmission shift is commanded while theengine is restarted.

Now turning to FIGS. 4-5, example restart sequences are depicted. Inparticular, map 400 of FIG. 4 depicts an engine restart where the enginerestart coincides with a transmission shift and the engine restart speedis adjusted based on the predicted gear after the shift. In comparison,map 500 of FIG. 5 depicts an engine restart where the engine restartspeed is adjusted based on the current gear.

Map 400 depicts a transmission gear selection at plot 401, atransmission input shaft speed at plot 402 (solid line) relative to anengine speed at plot 403 (dashed line), an engine torque at plot 406, adisconnect clutch pressure at plot 408, an engine restart command atplot 410, spark timing adjustments at plot 412, throttle openingadjustments at plot 414, and engine fueling at plot 416. All plots arerepresented over time (increasing along the x-axis from the left side tothe right side of each plot).

Prior to t1, the hybrid vehicle may be operating in an electric modewith the vehicle being propelled using motor torque. In addition, basedon vehicle operating conditions, the fixed gear ratio transmission maybe in a first gear (gear_1).

At t1, there may be a change in operator pedal position to a positionrequiring more torque. Herein, the torque demand may not be met by onlythe motor torque and additional engine torque may be required. Thus, att1, in response to the increase in torque demand, an engine restartcommand may be delivered and an engine restart event may be initiated.

In response to the engine restart command, between t1 and t2, the enginemay be cranked via the motor. Before t1, the disconnect clutch may befully open or held at a minimum degree of engagement, such as at astroke pressure 409. Between t1 and t2, the disconnect clutch may betransiently closed or partially engaged (as indicated by the transientincrease in clutch pressure) so as to enable the motor torque to be usedto bump up the engine speed to a first speed wherefrom combustion can beinitiated. As such, the disconnect clutch may have been held at strokepressure 409 prior to the engine restart to allow the motor to propelthe vehicle.

Also between t1 and t2, concurrent to the engine restart event, atransmission downshift is commanded. In particular, a transmission shiftfrom the first gear (gear_1) to a second, lower gear (gear_2) iscommanded. It will be appreciated that as used herein, first gear andsecond gear are used to refer to the order in which gears are selectedrather than the gear itself. In other words, the first gear is a firstgear selected on the transmission while the second gear is a subsequentgear selected on the transmission. As such, the first gear may be atransmission second gear, or an alternate, higher transmission gear.Likewise, the second gear may be a transmission first gear or analternate, lower transmission gear.

At t2, once the engine has been sufficiently cranked to a first speed bythe motor, engine fueling is resumed and cylinder combustion isinitiated. Thereafter, combustion torque is used to spin the engine.While the engine is combusting, the disconnect clutch is partiallydisengaged via increased clutch slippage. For example, the disconnectclutch pressure may be reduced to stroke pressure 409. In response toengine fueling, engine torque output may start to increase. However, dueto the engine speed not yet matching the synchronous motor speed, thedisconnect clutch is not fully engaged.

After t2, the engine may be in speed control. In particular, the enginetorque is commanded initially to a high value to overcome engine inertiaand accelerate the engine toward the engine target speed (as indicatedby first portion of plot between t2 and t3 having a steeper slope).However, the engine speed control is them modified to achieve the targetlower transmission input shaft speed 403 corresponding to Gear_2 of thetransmission shift, rather than the higher transmission input shaftspeed corresponding to Gear_1 of the transmission shift. That is, theengine speed control is adjusted to as a function of the predictedsynchronous motor speed 403 of the future gear engaged after thetransmission shift rather than the current gear engaged before thetransmission shift. As such, the engine speed is also adjusted based onthe engine maximum torque available for acceleration and the engineinertia.

As indicated, the initial engine speed control is achieved by openingthe throttle more and retarding spark from MBT. Thereafter, the enginespeed is controlled to the lower target speed by opening the throttleless and advancing spark towards MBT.

In particular, the spark and throttle adjustment performed to controlthe engine speed to target synchronous motor speed 403 may be based onthe impeller speed across the disconnect clutch. In particular, at lowerimpeller speeds, spark timing retard may be increased (e.g., spark maybe heavily retarded) and throttle opening may be decreased (e.g.,throttle may be closed on every event) to avoid raising the engine speedabove the target speed for improved driveability. In comparison, athigher impeller speeds, spark timing retard may be decreased (e.g.,spark may be advanced) and throttle opening may be increased (e.g.,throttle may be opened on every event) to raise the engine speed to thetarget speed quickly.

At t3, the engine may attain the synchronous speed of the motor.Consequently, between t3 and t4, the disconnect clutch pressure isincreased so that the clutch can be closed at t4. Thereafter, enginetorque may be used to propel the vehicle, while maintaining thetransmission in the second gear.

Now turning to FIG. 5, map 500 depicts a transmission gear selection atplot 501, a transmission input shaft speed at plot 502 (solid line)relative to an engine speed at plot 503 (dashed line), an engine torqueat plot 506, a disconnect clutch pressure at plot 508, an engine restartcommand at plot 510, spark timing adjustments at plot 512, throttleopening adjustments at plot 514, and engine fueling at plot 516. Allplots are represented over time (increasing along the x-axis from theleft side to the right side of each plot).

In FIG. 5, as in FIG. 4, prior to t11, the hybrid vehicle may beoperating in an electric mode with the fixed gear ratio transmission inthe first gear (gear_1). Then, at t11, due to a change in operator pedalposition, an engine restart command may be delivered and an enginerestart event may be initiated. Between t11 and t12, the engine may becranked via the motor with the disconnect clutch held at stroke pressure409. Between t11 and t12, the disconnect clutch may be partially engaged(as indicated by the transient increase in clutch pressure) so as toenable the motor torque to be used to bump up the engine speed to afirst speed wherefrom combustion can be initiated. As such, thedisconnect clutch may have been held at stroke pressure 409 prior to theengine restart to allow the motor to propel the vehicle.

Herein, between t11 and t12, no transmission shift is commanded, and thetransmission may remain in the first gear (gear_1) for the entirety ofthe engine restart event. At t12, once the engine has been sufficientlycranked to a first speed by the motor, engine fueling is resumed andcylinder combustion is initiated. Thereafter, combustion torque is usedto spin the engine. While the engine is combusting, the disconnectclutch is partially disengaged via increased clutch slippage. Forexample, the disconnect clutch pressure may be reduced to strokepressure 409. In response to engine fueling, engine torque output maystart to increase. However, due to the engine speed not yet matching thesynchronous motor speed, the disconnect clutch is not fully engaged.

After t12, the engine may be in speed control. In particular, the enginetorque is commanded to a high value to overcome engine inertia andaccelerate the engine toward the higher engine target speedcorresponding to Gear_1 of the transmission. That is, the engine speedcontrol is adjusted to as a function of the current synchronous motorspeed 503 (which is higher than the synchronous motor speed (403) ofGear_2 of the example of FIG. 4). As such, the engine speed is alsoadjusted based on the engine maximum torque available for accelerationand the engine inertia.

As indicated, the engine speed control to the higher target speed 503 isachieved by opening the throttle more and retarding spark from MBT. Oncethe target engine speed is approached or reached, spark timing isreturned to MBT and throttle opening is adjusted based on engine torquerequirement.

In particular, the spark and throttle adjustment performed to controlthe engine speed to target synchronous motor speed 503 may be based onthe impeller speed across the disconnect clutch. In particular, at lowerimpeller speeds, spark timing retard may be increased (e.g., spark maybe heavily retarded) and throttle opening may be decreased (e.g.,throttle may be closed on every event) to avoid raising the engine speedabove the target speed for improved driveability. In comparison, athigher impeller speeds, spark timing retard may be decreased (e.g.,spark may be advanced) and throttle opening may be increased (e.g.,throttle may be opened on every event) to raise the engine speed to thetarget speed quickly.

At t13, the engine may attain the synchronous speed of the motor.Consequently, between t13 and t14, the disconnect clutch pressure isincreased so that the clutch can be closed at t14. Thereafter, enginetorque may be used to propel the vehicle, while maintaining thetransmission in the first gear.

It will be appreciated that while the example of FIGS. 4-5 show distinctengine speed run-ups with and without transmission shifts, in stillother examples, the same engine run-up may include both conditions. Forexample, an engine may be restarted with no transmission shift pendingand the engine speed control may be adjusted to attain a first targetspeed that corresponds to a first predicted transmission input shaftspeed based on a current gear ratio. Thus, spark and throttle may becontrolled to run-up the engine speed to the first target speed.However, in response to a transmission shift occurring while the engineis being restarted and the engine speed is being run-up to the firsttarget speed, the controller may readjust the target speed to a secondtarget speed that corresponds to a second predicted transmission inputshaft speed based on the future gear ratio. The second target speed maybe higher or lower than the first target speed based on the future gearratio relative to the current gear ratio. Accordingly, spark andthrottle may be modified during the run-up to the first target speed soas to attain the second target speed. For example, spark and throttlemay be adjusted differently to attain the higher or lower target speedas compared to the target speed applicable when there was no gear shift.As an example, the first target speed may be a higher target speedcorresponding to a higher current gear ratio. Thus, a larger throttleopening and a higher amount of spark retard may be applied during therestart to run-up the engine speed to the first target speed. Inresponse to a transmission downshift occurring before the first targetspeed is reached, the throttle opening and the spark retard may bedecreased to modify the engine speed run-up trajectory to a secondtarget speed, lower than the first target speed, wherein the secondtarget speed corresponds to a lower future gear ratio of thetransmission downshift. In an alternate example, in response to atransmission upshift occurring before the first target speed is reached,the throttle opening and the spark retard may be further increased tomodify the engine speed run-up trajectory to a second target speed,higher than the first target speed, wherein the second target speedcorresponds to a higher future gear ratio of the transmission upshift.

As an example, a hybrid vehicle system may comprise an electric motor;an engine; a disconnect clutch coupled in a driveline between the engineand the motor; vehicle wheels configured to receive propulsion powerfrom one or more of the engine electric motor and the engine via thedriveline; and a fixed gear transmission including a plurality of gears,the transmission coupled to the driveline between the electric motor andthe vehicle wheels. The vehicle system may further include a controllerincluding non-transitory executable instructions for: in response to afirst engine restart during a transmission shift, adjusting an enginespeed during engine restarting based on a future gear of thetransmission; and in response to a second engine restart outside of atransmission shift, adjusting the engine speed during the enginerestarting based on a current gear of the transmission. Herein,adjusting the engine speed based on the future gear during the firstrestart includes adjusting the engine speed to match a transmissioninput shaft speed predicted based on the future gear, the predictedtransmission input shaft speed lowered when the future gear is lower,the predicted transmission input shaft speed raised when the future gearis higher. In comparison, adjusting the engine speed based on thecurrent gear during the second restart includes adjusting the enginespeed to match a transmission input shaft speed predicted based on thecurrent gear.

The controller may include further instructions for, during both thefirst and second engine restarts, maintaining the disconnect clutch atleast partially open until the engine speed matches the predictedtransmission input shaft speed, and then closing the disconnect clutch.During the first engine restart, after closing the disconnect clutch,the controller may fully engage the future gear. During both the firstand second engine restarts, the controller may adjust spark timing andthe position of an intake throttle based on an impeller speed estimateddownstream of the motor. The impeller speed may correspond to the outputof the motor speed and the input of a torque converter impeller coupledalong the driveline between the motor and the transmission. Inparticular, during both restarts, spark timing may be retarded and thethrottle may be moved to a more closed position when the impeller speedis lower. In comparison, the spark timing may be advanced and thethrottle moved to a more open position when the impeller speed ishigher.

The technical effect of adjusting engine speed control during an enginerestart to match a target synchronous motor based on a future gear of atransmission shift occurring concurrent to the restart is that drivelinetorque disturbances and related NVH issues can be reduced. As such, thisreduces the occurrence of vehicle lurches and stalls. In addition,engine restart and vehicle transition from electric mode to hybrid modecan be achieved substantially seamlessly, with no disturbance to thevehicle operator, even if the operator changes torque demand while theengine is being restarted. That is, engine restarts and transmissionshifts can be performed concurrently. By adjusting spark timing andthrottle opening during the engine run-up speed control based on animpeller speed estimated downstream of the vehicle's motor, enginedriveability at lower impeller speeds is improved while allowing thetarget engine speed to be attained rapidly at higher impeller speeds. Byreducing engine restart NVH issues, overall engine restart quality isimproved and the operator's drive experience is enhanced.

Note that the example control and estimation routines included hereincan be used with various engine and/or vehicle system configurations.The control methods and routines disclosed herein may be stored asexecutable instructions in non-transitory memory. The specific routinesdescribed herein may represent one or more of any number of processingstrategies such as event-driven, interrupt-driven, multi-tasking,multi-threading, and the like. As such, various actions, operations,and/or functions illustrated may be performed in the sequenceillustrated, in parallel, or in some cases omitted. Likewise, the orderof processing is not necessarily required to achieve the features andadvantages of the example embodiments described herein, but is providedfor ease of illustration and description. One or more of the illustratedactions, operations and/or functions may be repeatedly performeddepending on the particular strategy being used. Further, the describedactions, operations and/or functions may graphically represent code tobe programmed into non-transitory memory of the computer readablestorage medium in the engine control system.

It will be appreciated that the configurations and routines disclosedherein are exemplary in nature, and that these specific embodiments arenot to be considered in a limiting sense, because numerous variationsare possible. For example, the above technology can be applied to V-6,I-4, I-6, V-12, opposed 4, and other engine types. The subject matter ofthe present disclosure includes all novel and non-obvious combinationsand sub-combinations of the various systems and configurations, andother features, functions, and/or properties disclosed herein.

The following claims particularly point out certain combinations andsub-combinations regarded as novel and non-obvious. These claims mayrefer to “an” element or “a first” element or the equivalent thereof.Such claims should be understood to include incorporation of one or moresuch elements, neither requiring nor excluding two or more suchelements. Other combinations and sub-combinations of the disclosedfeatures, functions, elements, and/or properties may be claimed throughamendment of the present claims or through presentation of new claims inthis or a related application. Such claims, whether broader, narrower,equal, or different in scope to the original claims, also are regardedas included within the subject matter of the present disclosure.

The invention claimed is:
 1. A vehicle system, comprising: an electricmotor; an engine including an intake throttle and a spark plug; adisconnect clutch coupled in a driveline between the engine and themotor; vehicle wheels configured to receive propulsion power from one ormore of the electric motor and the engine via the driveline; a fixedgear transmission including a plurality of gears, the transmissioncoupled to the driveline between the electric motor and the vehiclewheels; and a controller including non-transitory executableinstructions for: in response to a first engine restart during atransmission shift, adjusting an engine speed during engine restartingbased on a future gear of the transmission; and in response to a secondengine restart outside of the transmission shift, adjusting the enginespeed during the engine restarting based on a current gear of thetransmission.
 2. The system of claim 1, wherein adjusting the enginespeed based on the future gear during the first engine restart includesadjusting the engine speed to match a transmission input shaft speedpredicted based on the future gear, the predicted transmission inputshaft speed raised when the future gear is lower, the predictedtransmission input shaft speed lowered when the future gear is higher,and wherein adjusting the engine speed based on the current gear duringthe second engine restart includes adjusting the engine speed to matchthe transmission input shaft speed predicted based on the current gear.3. The system of claim 2, wherein the controller includes furtherinstructions for, during both the first and second engine restarts,maintaining the disconnect clutch at least partially open until theengine speed matches the predicted transmission input shaft speed, andthen closing the disconnect clutch; and adjusting spark timing andthrottle position based on an impeller speed estimated downstream of themotor, the spark timing retarded and the throttle moved to a more closedposition when the impeller speed is lower, the spark timing advanced andthe throttle moved to a more open position when the impeller speed ishigher.
 4. The system of claim 3, wherein the controller includesfurther instructions for, during the first engine restart, after closingthe disconnect clutch, fully engaging the future gear.